There is considerable interest nowadays in modifying the seed oil fatty acid composition and content of oilseeds by molecular genetic means to provide a dependable source of Super High Erucic Acid Rapeseed (SHEAR) oil for use as an industrial feedstock. A similar interest exists for producing other strategic non-edible oils (e.g. seed oils high in hydroxy-, epoxy-, short and medium chain fatty acids, etc.) in traditional oilseed crops (e.g. rapeseed, flax, sunflower, soybean).
For edible oils, there is considerable interest in changing the fatty acid composition (e.g. higher oleic/lower polyunsaturates, lower saturates, higher saturates) as well as increasing the oil content in oilseed crops such as Canola and edible oil flax (Linola), soybean and sunflower.
Currently, there are no documented demonstrations of increases in oil content (yield) by transgenic means, although yield increases by traditional breeding and selection continue to bring about incremental improvements.
In contrast, increases in the proportions of some strategic fatty acids have been achieved by the introduction of various plant fatty acid biosynthesis and acyltransferase genes in oilseeds. Some examples of such processes are the following:
1. Expression of a medium chain fatty acyl-ACP thioesterase from California Bay, in Brassicaceae to increase the lauric acid (12:0) content (Calgene; Voelker et al., 1992; 1996--see References 35 and 36 in the accompanying "References Pertinent to the Present Invention"). PA1 2. Expression of a Jojoba .beta.-ketoacyl-CoA synthase in low erucic acid Brassica napus (Canola) cultivars to increase the level of erucic acid; the effect following expression in high erucic acid cultivars was negligible (Calgene; Lassner et al., 1996--see Reference 20). PA1 3. Expression of an anti-sense construct to the stearoyl-ACP .DELTA.9 desaturase in Brassicaceae to increase the stearic acid content (Calgene; Knutzon et al., 1992--see Reference 16). PA1 4. Increased proportions of oleic acid in B. napus by co-suppression using a sense construct encoding plant microsomal FAD2 (.DELTA.12) desaturase (duPont/InterMountain Canola; Hitz et al., 1995--see Reference 12). PA1 5. Increased proportions of 12:0 or 22:1 in the sn-2 position of triacylglycerols (TAGs) in rapeseed by expression of coconut or meadowfoam lyso-phosphatidic acid acyltransferases (LPATs; E.C. 2.3.1.51), respectively (Calgene; Knutzon et al., 1995 a & b;--see References 17 and 18; Lassner et al., 1995--see Reference 21).
Although the use of plant transgenes resulted in altered proportions of sn-2 lauric and erucic acids, in laurate canola and high erucic acid rapeseed, respectively, the overall proportions of lauric and erucic acids in the seed oil were not increased, and there was no evidence of increased total fatty acid content, or increased oil yield in these transgenics.
There is accordingly a need for new ways of increasing oil yield and improving oil composition in oilseed plants by employing genetic engineering techniques.